Characterization of two RNAs transcribed from the cis-regulatory region of the abd-A domain within the Drosophila bithorax complex.

The infra-abdominal (iab) regions of the biothorax complex are thought to cis-regulate expression of the abdominal-A (abd-A) and Abdominal-B (Abd-B) transcripts. These large cis-regulatory regions are also actively transcribed. Here we present a detailed analysis of the transcription products of the iab-4 region. During early embryogenesis a 6.8-kilobase (kb) RNA is transcribed and processed to yield 1.7- and 2.0-kb poly(A)+ RNAs. These RNAs are expressed from the time of cellular blastoderm formation to germ-band shortening and are localized in parasegments 8-14 (the posterior second through the anterior ninth abdominal segments). Sequence analysis of the two RNAs suggests that they may not be translated. We discuss some possible functions of the 1.7/2.0-kb iab RNAs and the significance of their similarity to the bithoraxoid (bxd) RNAs and other transcripts from the iab regions of the abd-A and Abd-B domains.